1. Field of the Invention
The invention relates to a method for removing defects in the crystal lattice of silicon wafers cut from rod-like structures and into which doping materials are diffused at a predetermined temperatures.
2. Description of the Prior Art
Semiconductor components such as thyristors, GTO (gate turn-off) thyristors and diodes use semiconductor wafers that are cut from drawn monocrystalline silicon rods. Typically, the wafers are cut from the rods using a precision saw. Evaluations of such semiconductor wafers have shown that a significantly higher defect density is present in the central region of the wafers. These defects have a high probability of being accumulations of vacancies or voids, caused by the drawing process of the crystal.
If doping materials are diffused into such semiconductor wafers at a high temperature, e.g. 1240.degree. C., heavy metals can settle or accumulate in these vacancies or voids. As a result, imperfections arise that lie deep in the silicon energy band. Such imperfections result in a reduced charge carrier lifetime within these central regions of the wafers. Consequently, high leakage currents can be generated, particularly for power semiconductors with significantly higher silicon thicknesses and considerably deeper space charge regions than other types of semiconductor components.
Accordingly, there is a need for a method for removing defects such as voids or vacancies in the central regions of silicon wafers that result in accumulated heavy metals in the central regions of silicon wafers.